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Yet the frequency of these shakes has declined in recent months—and no traditional quakes rumbled there when the mystery waves began on November The French Geological Survey BRGM is closely monitoring the recent shaking, and it suggests that a new center of volcanic activity may be developing off the coast. Mayotte was formed from volcanism, but its geologic beasts haven't erupted in over 4, years.
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Instead, BRGM's analysis suggests that this new activity may point to magmatic movement offshore—miles from the coast under thousands of feet of water. Though this is good news for the island inhabitants, it's irksome for geologists, since it's an area that hasn't been studied in detail. Since mid-July, GPS stations on the island have tracked it sliding more than 2. The early period of rumbling was also overprinted with what seemed to be the P- and S- waves of tiny tremors, explains Lomax, who spotted the faint pings by filtering out the low-frequency signals.
Such pings are commonly associated with magma moving and fracturing rock as it squirts through the crust. But even those signals were a little strange, says Helen Robinson , a Ph.
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It passed by largely unnoticed, he suggests, because it was what's known as a slow earthquake. These quakes are quieter than their speedy cousins since they come from a gradual release of stress that can stretch over minutes, hours, or even days.
These slow types of quakes are often associated with volcanic activity. At the Mount Nyiragongo volcano in the Democratic Republic of Congo, a similar slow earthquake and low-frequency waves were linked with a magma chamber collapsing. Slow quakes were also stunningly frequent during the most recent fiery run of Kilauea in Hawaii , which produced nearly 60 of these events between May and the end of July, sending seismic waves around the world.
So what is actually causing the super-slow vibrations at Mayotte? A submarine eruption could produce these low rumblings, but evidence for such an event has yet to materialize. Most current guesses revolve around resonance in a magma chamber, triggered by some type of subsurface shift or chamber collapse. Studying the intricate features of the seismic waves could yield clues to the size and shape of the molten material lurking below. The signal's odd uniformity could be due, in part, to the surrounding rocks and sediments, Lomax adds.
Perhaps the local geology is filtering the sounds and only letting this single second wave period escape.
Robinson agrees with this idea, noting that the geology here is extremely complex. Mayotte sits in a region crisscrossed by ancient faults—including fracture zones from the final breakup of the southern supercontinent Gondwana. What's more, the underlying crust is somewhat transitional, shifting between the thick continental crusts and the thinner oceanic crusts. Perhaps this complexity drives the simplicity of the escaping waves, Robinson says. For now, though, the lack of data makes it tough to say more about the wiggly forms.
Hicks' preliminary models hinted that the waves emanated from subsurface inflation, rather than a magma chamber draining or collapsing.
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But with a little additional data, the model flipped and pointed to chamber deflation instead. Or sometimes they can alternate, pumping up and down like Earth's fiery lungs. BRGM plans to do ocean bottom surveys to get more detailed information about the region and investigate the possibility of a submarine eruption. In the meantime, the seismic sleuthing continues with the data that's available. Whether the cause is ordinary or extraordinary remains to be seen, Lomax says, but the science—and the fun—is in the chase.
That's the way it should go. That's scientific advance. Read Caption. But scientists are yet to find the reason behind the increase. One reason could be different parts of the earth warming at different rates; it is likely to bring frequent changes in air circulation see ' Rain Shocked ', Down to Earth , March , The different rate of heating could be due to both local factors and global warming. The decade , during which the frequency of heat waves increased sharply, was the warmest in the past years.
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